192 INTERNAL ANATOMY OF INSECTS. 
rises ami falls ; it bends in various directions ; and its 
segments can often be lengthened or retracted. Besides 
all this, its spiracles open and shut, and its reproductive 
and other anal organs have their appropriate motions. 
In numerous Coleoptcra, however, and some Hemiptera^ 
the upper-side of the abdomen is almost the only part 
that is moveable, especially near the trunk ; the under- 
side, having its first segments soldered together, is only 
capable of motion near the tail 3 . The muscles that pro- 
duce the various motions of this part must be entitled to 
all the denominations stated above b . I have on a former 
occasion explained to you how, in insects that have a 
petiolate abdomen, that part is elevated and depressed . 
In those with a sessile one the base is attached to the 
metaphragm by strong ligaments' 1 , and the muscles that 
move the first piece act from one segment to another. 
The partial movements of the segments of this part, 
where they have place, are produced by muscular fibres 
which extend from the whole anterior margin of one to 
the whole posterior one of that which precedes it. If 
those, for example, of the back contract, the abdomen 
becoming shorter above, bends upwards; and if those 
of the sides or belly, it bends sideways or downwards : 
this is a beautiful as well as simple contrivance. 
The alternate rush of air from the abdomen into the 
alitrunk, and from the atmosphere into the abdomen, is 
attended by the constriction or expansion of that part 
a Chabrier Sur le Vol des Ins. c. i. Addend. 298. 
b See above, p. 178 — . 
c Vol. III. p. 700—. 
d Chabr. ubi svpr. c. i. 422. 
e Cuv. Anal. Com p. i. 451. 
